The subject invention relates generally to an improved spray gun utilizing coating material with a wide range of conductivity in an electrostatic spray coating system. More specifically, the subject invention relates to a rotary spray gun capable of improving the transfer efficiency of the coating by generating ionic lines to shape the spray pattern of the coating material being atomized by the spray gun.
Apparatus used for electrostatically coating objects such as, for example, an automobile body, have been in use for some time. Primarily, a voltage potential is applied to a spray head of a rotary atomizer in order to produce an electric field between the spray head and a grounded object to be coated. The charge generated by the spray head is transferred to the atomized coating material by direct contact as it is radially disbursed from the spray head.
An additional charge ring has been added to the spray apparatus primarily, for water borne coating materials. The charge ring typically includes a plurality of electrodes concentrically aligned with the axis of the spray head. The electrodes are generally coated with an insulating material, with a small pin protruding therefrom. A high voltage cable specifically supplies the electrical potential to the electrodes necessary for generating an electrical field for charging the particles sprayed from the spray head. Often, the electrodes will be charged to generate the electric field, and the spray head will be grounded. In this type of arrangement, the entirety of the electrostatic charge transferred to the coating material is generated from the electrodes concentrically aligned with the spray head.
While this type of electrostatic arrangement has proven quite effective for water borne based coating materials, it is not proven to be as effective for solvent borne coating materials. Therefore, the entirety of the electrostatic charge transferred to atomized particles in a solvent borne coating system is derived from the rotary spray head that has an electrical potential less than ground. Frequently, the mass of an atomized coating particle is too large when radially disbursed from the spray head will derive a physical potential greater than the electrical potential produced from the spray head. When this occurs, the atomized particle will be thrown laterally from the spray head and thus, will not be directed toward the grounded object to be painted. The frequency from which this happens is known to reduce the transfer efficiency of the atomized coating material onto the object to be painted.
Accordingly, it would be desirable to introduce an ionization ring to a solvent borne painting apparatus that can generate an ionic field capable of overcoming the momentum of the atomized coating particles that are disbursed laterally from the spray head.
The present invention comprises an apparatus for electrostatically coating objects with an electrically conductive coating material capable of carrying an ionic charge. A rotary atomizer utilizes a spray head that rotates on an axis at a high speed. An external housing is affixed to a support member that is oriented either horizontally or vertically depending upon the application needs of the object to be coated. The external housing pivotally supports the spray head and includes a non-conductive surface. Conductive elements such as a limb or structural band are disposed upon the housing. The conductive elements derive electrical potential that is generally the same as the electrical potential of the spray head. The non-conductive surface of the housing is at neutral potential relative to the potential of the spray head and the conductive elements.
An ionizing device is positioned on the housing to contact the conductive elements. Thus, the ionizing device derives an electrical potential that is generally the same as the spray head and the conductive elements. A halo with a plurality of generally conical members spaced therearound directs ionizing lines to shape the atomized coating material being radially disbursed from the spray head.
The generally conical members generate ionic lines at substantially the same potential as the spray head and the conductive elements. The ionic lines are disbursed at an electric potential strong enough to overcome the momentum of many of the electrostatically charged, atomized particles being radially disbursed from the spray head thereby forcing these atomized particles toward the grounded object to be painted. Therefore, the ionic lines generated from the generally conical members improve the transfer efficiency of the coating material dispersed from the spray head onto the object to be painted. Further, it should be understood by those of skill in the art that a reduction in the amount of shaping air necessary to shape the atomized particles can be achieved through the utilization of the improved ionic field generated by the inventive ionization ring. Through the reduction of shaping air, a reduction in dirt trapped in the paint coating can also be achieved due to the reduction in air turbulence in the paint booth.